8.8 Windows Boot Errors

Use the following recommendations to troubleshoot startup errors with the advanced boot options.

* Boot into Safe Mode and then use the appropriate tool to undo any recent changes. For example, you can: - Use Device Manager to roll back drivers or disable devices that might be causing the problem. - Use Add or Remove Programs to uninstall software that has just been added. - Restore any settings that may have changed. - Disable unneeded services or applications that load at startup. - Use System Restore to restore the system to a known good restore point. * After booting into Safe Mode, begin by undoing the most recent change to the system. - For example, if the problem started after installing a new device driver, roll back the driver and reboot. * If undoing recent changes does not fix the problem, you could disable all unnecessary devices and services. If you can boot normally, you can identify the component that was causing the problem by enabling devices and services one-by-one until the system becomes unstable.

Troubleshooting Startup Errors with (Safe Mode)

1. Boot into Safe Mode and then use the appropriate tool to undo any recent changes. For example, you can: * Use Device Manager to roll back drivers or disable devices that might be causing the problem. * Use Add or Remove Programs to uninstall software that has just been added. * Restore any settings that may have changed. * Disable unneeded services or applications that load at startup. * Use System Restore to restore the system to a known good restore point. 2. After booting into Safe Mode, begin by undoing the most recent change to the system. - For example, if the problem started after installing a new device driver, roll back the driver and reboot. 3. If undoing recent changes does not fix the problem, you could disable all unnecessary devices and services. If you can boot normally, you can identify the component that was causing the problem by enabling devices and services one-by-one until the system becomes unstable.

Boot Device Selection (BDS)

A UEFI boot process phase - A GPT or MBR determination is made based on boot configuration. * If an EFI System Partition (ESP) exists, the following process occurs: 1. On the ESP in the \EFI\Microsoft directory, the boot manager looks for and runs the bootmgfw.efi file. 2. The bootmgfw.efi looks for the BCD store in the same directory containing a list of all Windows installations. 3. If only one installation exists, UEFI automatically loads it. If multiple installations exist, a list of bootable operating systems displays. * If no ESP exists, the boot manager uses Legacy BIOS mode to complete the boot sequence: 1. The MBR looks for and loads the bootmgr.exe program. 2. The bootmgr.exe program looks for the BCD store in either the C:\ directory or the System Reserved partition. 3. If only one installation exists, bootmgr.exe automatically loads the OS. If multiple installations exist, a list of bootable operating systems displays. !! At the beginning of the BDS stage, the UEFI interface executes. The option to load the EFI Shell or enter the UEFI configuration is available.

Run Time (RT)

A UEFI boot process phase - After the operating system and devices are configured, the system waits for user logon. Following logon, the operating system is configured with user-specific settings. 1. Control of the system passes to ntoskrnl.exe. 2. The Windows logo displays and ntoskrnl.exe: - Loads device drivers. - Starts services. - Configures the OS environment. 3. The wininit and winlogon programs run to allow user logon. The Welcome screen displays. 4. Following logon, all remaining device drivers and user settings load. In addition, the current configuration profile copies to the Last Known Good Configuration registry. !! Even though it has more stages, the UEFI boot sequence is considerably faster than the BIOS boot sequence.

Transient System Load (TSL)

A UEFI boot process phase - Depending on the boot device selected, the firmware boots an OS loader, UEFI Shell, or UEFI application. 1. The BCD store identifies the location of the operating system loader (for Windows, the default location is C:\Windows\system32\winload.efi). 2. The operating system loader winload.efi is started. 3. Winload.efi then loads the following elements: - System registry. - Ntoskrnl.exe. - Essential device drivers.

non-system disk error

A common cause of the non-system disk error is leaving a USB device plugged in. You can avoid these errors by disabling the USB Device option in the boot sequence or setting the integrated USB controller to No Boot.

bootrec /rebuildbcd

Adds missing Windows installations to the BCD

Logon and user configuration

After configuring the operating system and devices, the system waits for user logon. Following logon, the operating system is configured with user-specific settings. 1. The wininit and winlogon programs run to allow user logon. At this point, the Welcome or user logon screen displays. 2. Following logon, all remaining device drivers and user settings load. In addition, the current configuration profile is copied to the Last Known Good Configuration registry.

boot loader

An operating system program responsible for managing the process of loading the OS during the boot.

Corrupt boot sector

At this point in the process, the MBR has loaded, located an active partition, but there is a problem in loading the VBR: either the VBR does not specify a boot loader program or the boot loader specified in the VBR is missing or corrupt. Symptoms of a corrupt or missing boot sector include: * System hangs following the BIOS information screen. * Any of the following errors: - Non-system disk or disk error. - Remove disks or other media. - Invalid system disk. - Invalid media type. - Disk boot failure. - A disk read error occurred. - BOOTMGR is missing. - Missing GRUB/LILO. To correct the problem, you can check the boot order in the BIOS/UEFI to make sure the system is booting from the correct storage device. Then, boot from the installation disk and repair the system. ! If the device is a removable media device, the drive should be empty (so the drive is skipped when checking for a boot disk) or the drive must have media that includes a bootable partition for the system to boot from that drive.

Boot Configuration Data (BCD)

Boot Configuration Data (BCD) is a firmware-independent database for boot-time configuration data used by Microsoft's Windows Boot Manager found with Windows Vista, Windows 7, and Windows Server 2008.

You experience startup errors after you install a new device. What should you do FIRST to resolve the issue? Recover the system image. Boot in Safe Mode and roll back the driver. Boot in Safe Mode and disable all unnecessary devices. Disable automatic restart.

Boot in Safe Mode and roll back the driver. Explanation If you experience startup errors after you install a new device, the first thing you should do is boot in Safe Mode and roll back the driver. You should not disable unnecessary devices, disable automatic restart, or recover a system image before trying other options.

Rodney, an employee in the Research Department, reports that he is experiencing blue screen errors while using his Windows computer. You ask Rodney if anything has changed on the computer recently. Rodney explains that he recently installed a TV tuner board in an expansion slot, and now he has to reboot the computer every time he loads the TV tuner application to watch TV. You need to fix Rodney's computer and prevent him from using the TV until you can install an updated driver. What should you do? Reboot the system and select Safe Mode. Edit the properties of the TV tuner driver in Device Manager and select Roll Back Driver. Use the Reset This PC option in the Settings app. Boot the system from a Windows installation disc and select the Startup Repair option. Boot the system in Safe Mode. Disable the TV tuner driver in Device Manager. Re-install Windows from the installation disc.

Boot the system in Safe Mode. Disable the TV tuner driver in Device Manager. Explanation You should disable the driver in Safe Mode instead of rolling the driver back. Although you might be able to disable the driver without booting in Safe Mode, booting in Safe Mode is a good way to prevent drivers that could interfere with your task. Resetting or reinstalling the operating system are drastic troubleshooting options. You should try simpler resolutions first before resorting to more aggressive options. Because the boot process is functioning, there is no indication that the boot sector or Master Boot Record need repairs.

Disable Automatic Restart on System Failure

By default, Windows reboots whenever a critical system error occurs (e.g., blue screen of death). * You have only a short time before the system reboots when the error occurs. This might not be sufficient time to read and record the error information. * If the error occurs while you are away from the computer, you will see a message that the system restarted, but won't have seen the error. * If the error occurs during startup, the system might continually reboot. Use this option on the advanced boot menu to stop the automatic reboots.

What should you do if you hear a series of beeps when the system powers on and nothing displays on the monitor?

Check Hardware 1. Check the keyboard to ensure that there are no stuck keys and no keys are being held down. Sometimes a keyboard drawer can press a key against the underside of a desk. Run your fingers over the keyboard to free any keys that may be stuck. If a drink was spilled on the keyboard, replace the keyboard with a new one. Try to start the computer again after completing this and each of the following steps. 2. Check all cables connected to the computer and make sure they are fully plugged in. Inspect each cable and securely connect or tighten cables as required. 3. Remove any objects blocking the computer's air vents. If dust has accumulated in any vent, vacuum the exterior vents and carefully vacuum dust from the heat sinks and vents inside the computer. 4. Disconnect external devices such as printers, USB sticks and hubs, remote receivers and external drives. If the computer starts without external devices connected, one of these components may be defective. Reconnect them one at a time to identify which device is defective. Beeping Computer Problems Due to Internal Components 1. Ensure that internal hardware added to your computer recently, such as additional memory or a video card, is installed correctly. Turn off the computer, then remove and re-insert the new hardware ensuring that each component is firmly seated in its slot. 2. Remove new internal hardware. If the computer starts without the component, it may be defective or incompatible with your computer. 3. Remove and re-insert all internal connectors and cards, including the memory but not the CPU. 4. If more than one memory card is installed in your computer, troubleshoot each card one at a time. Make sure each card is fully seated in its designated slot. 5. Disconnect all internal devices including hard drives, expansion cards, optical drives and card readers. If the computer starts without internal devices connected, one of them may be defective. Reconnect each device one by one to determine which one is defective.

Your system hangs immediately after the BIOS information is shown and displays an error loading operating system error message. What is the MOST likely source of the problem? Missing or corrupt file Corrupt MBR or partition table Corrupt boot sector Inaccessible boot disk

Corrupt MBR or partition table Explanation Symptoms of a corrupt MBR or partition table include the system hanging immediately after the BIOS information is shown and error messages such as missing operating system or MBR corrupt. A corrupt boot sector, inaccessible boot disk, or a missing or corrupt file are less likely to display this type of error message.

Driver Execution Environment (DXE)

DXE initializes configured devices, mounts drives, and prepares to boot the OS. 1. Device drivers load into memory. 2. Hardware devices (e.g., video card, network card, USB controllers) initialize simultaneously. 3. System drives mount and initialize. 4. The EFI boot manager initializes.

You have been troubleshooting startup errors on your Windows 11 computer by undoing recent changes, such as rolling back device drivers for a local printer and new graphics card while in Safe Mode. However, the changes you are making are not resolving the startup errors. Which of the following steps will MOST likely help you to find the specific cause of the error without the need to re-install Windows? Disable and then enable devices and services one by one. Launch and use the utilities provided in the Recovery Environment. Disable Driver Signature Enforcement. Disable automatic restart on system failure.

Disable and then enable devices and services one by one. Explanation If undoing recent changes does not fix the problem, you could disable all unnecessary devices and services. If you can boot normally, you can then identify the component that was causing the problem by enabling devices and services one by one until the system becomes unstable. While selecting the Disable Driver Signature Enforcement in Advanced Startup Options would cause Windows not to require a digital signature when loading a driver, this option would not help you find the specific driver or service that might be causing the startup error. While selecting the Disable automatic restart on system failure option in Advanced Startup Options would prevent Windows from restarting when a critical system error occurs, it would not help you find a specific driver or service that might be causing the startup error. The Recovery Environment provides tools such as System Restore, System Image Recovery, and Startup Repair, which could all potentially bring your Windows 11 system back to a usable state. However, the tools (by themselves) would not be very helpful in finding the specific cause of the startup error.

Boot loader

During the boot loader stage, the following process occurs: 1. On the boot device, the BIOS searches for and loads the boot code in the master boot record (MBR). The MBR is located in the first sector on the disk. 2. The MBR boot code uses the partition table to identify the active disk partition. 3. On the active partition, MBR boot code looks for and loads the bootmgr.exe program. 4. The bootmgr.exe program looks for the binary-coded decimal (BCD) store in either the C:\ directory or the System Reserved partition. The BCD store contains a list of all Windows installations on the disk. 5. If only one installation exists, bootmgr.exe automatically loads the operating system (OS). If multiple installations exist, it displays a list of bootable operating systems. !! This stage occurs after the BIOS information screen disappears but before the Windows loading screen displays.

OS Startup

During this stage, the operating system starts. The operating system configures system devices and loads necessary files. The following process occurs: 1. The operating system loader winload.exe starts. At this stage, you can access advanced startup options (e.g., safe mode) by pressing the F8 key (on most computers). winload.exe loads the following: - System registry. - Ntoskrnl.exe. - Essential device drivers. 2. Control of the system passes to ntoskrnl.exe. 3. At this point, the Windows logo displays and ntoskrnl.exe: - Loads device drivers. - Starts services. - Configures the OS environment

sfc /verifyfile

Identifies the integrity of the file specified, and makes any repairs or changes.

Service fails to start

If a service fails to start, you will see a message such as: "At least one service or driver failed during system startup. Use Event Viewer to examine the event log for details." Use Event Viewer to view details about the service that did not start. Then try starting the service manually. If necessary, re-enable or re-install the service.

Boot Options

If a system will not start or has significant problems, you can boot the system in various modes that may help you get the system up and running. There are two main ways you can select an alternate boot mode. - To restart the device to change startup settings, including starting from a disc or USB drive: - Select Start. - Select Settings. - Select System. - Under Recovery options, select Restart now. Alternately, you can run the msconfig.exe utility to specify the boot mode to use and then reboot the system.

Missing or corrupt file

If the boot manager cannot locate needed operating system files on the selected boot partition, you might see the following errors occur: • Windows could not start because the following file is missing or corrupt: <filename> Please re-install a copy of the above file. • A blue screen error that describes a corrupt or missing file. This problem is caused either by a corrupt disk, corrupt files, or missing files. To correct the problem, boot the system from the installation disc and repair the system. 1. Boot from the installation DVD (or the recovery USB). 2. At the Welcome screen, select Repair your computer. 3. Select Troubleshoot. 4. Select Advanced Options. 5. Select Startup Repair. Alternatively, you can select the Command Prompt option and then use the copy command to replace the file referenced by the error message with a known good copy.

System does not power on

If the system does not power on: • Make sure the system is plugged in and the power strip or UPS is turned on. • Check the power switch and the power type (110 or 220 volts) on the back of the power supply. • If your computer is a notebook or tablet, make sure the battery is installed. Ensure that the AC adapter is plugged in. • If you have just installed a new system, make sure the system case power switch is connected to the motherboard. When you turn on the computer, you should hear both the power supply fan and the CPU fan start to spin.

System powers on, but no display is visible

If the system powers on but there is nothing on the display, check the following: • Verify that the monitor is connected to the computer, plugged in, and turned on. • Verify that the BIOS/UEFI is configured to use the correct video adapter. Most motherboards can be configured to use either the integrated video adapter or a PCIe video adapter installed in an expansion slot. • To display startup information on the screen, the computer needs at a minimum the CPU, memory, and a video card. Other components are not necessary. Verify that these three components are properly installed. • If necessary, reduce the system to the three components listed above and try starting the system. If that does not work, swap out components to identify the failed component. Some computers will use a series of beeps to indicate specific problems when those messages cannot be shown on the screen. In this case, consult the motherboard documentation for the meaning of the audible messages.

Corrupt or missing DLL or system file

If you see errors about corrupt or missing DLLs or system files, either during startup or after Windows starts, boot the system from the installation disc and repair the system. 1. Boot from the installation DVD (or the recovery USB). 2. At the Welcome screen, select Repair your computer. 3. Select Troubleshoot. 4. Select Advanced Options. 5. Select Startup Repair. Alternatively, you can select Command Prompt and use the sfc command to run the System File Checker utility. The syntax to use with sfc is as follows: • Use sfc /scannow to scan the integrity of all protected system files and repair any file that has problems. • Use sfc /verifyonly to scan the integrity of all protected system files, but not repair them. • Use sfc /scanfile to scan the integrity of a specific file and repair it if it has problems. • Use sfc /verifyfile to scan the integrity of a specific file, but not repair it.

Security (SEC)

Immediately after the system is powered on, the SEC sequence begins. 1. Power is supplied to the CPU. 2. The CPU switches from 16-bit Real Mode to 64-bit Protected Mode. 3. The CPU executes a specific set of instructions to prepare the system for the Pre-EFI Initialization (PEI) to run.

boot sector (also called volume boot record)

It is responsible for loading the operating system boot loader program (BOOTMGR).

MBR (Master Boot Record)

It is responsible for locating the system (active) partition and loading the volume boot record (VBR). A corrupt or missing master boot record or a corrupt partition table prevents the system from loading the boot record code, finding the volume boot record, and loading the boot loader program.

You have booted your Windows workstation in Safe Mode and enabled boot logging. To which log file is the boot logging information now written? Bootlog.txt Myboot.txt Ntbtlog.txt Boot.log

Ntbtlog.txt EXPLANATION When you choose to enable boot logging, entries are written to the Ntbtlog.txt file. This file is created in the %WinDir% folder. Bootlog.txt, boot.log, and myboot.txt are not valid boot logging files.

POST (Power-On Self Test)

On a system using BIOS, the following steps take place: 1. Power is supplied to the CPU. The CPU is hard-coded to look at a particular memory address containing a printer (or jump program) that instructs the CPU where to find the BIOS program. 2. The CPU loads the BIOS program. The first BIOS process to run is the POST, which verifies the integrity of the BIOS code. POST also: - Locates, sizes, and verifies system memory. - Verifies and initializes video card (output displays on the monitor). - Identifies available hard disks. 3. After POST tests are complete, the BIOS: - Identifies other system devices. - Uses CMOS settings and information supplied by the devices to identify and configure hardware devices. - Allocates system resources to plug-and-play devices. Typically displays information about the keyboard, mouse, and SATA drives. 4. The BIOS then searches for a boot drive using the boot order specified in the CMOS. !! During this sequence, system information displays on the screen, and the option to enter the CMOS setup to configure system parameters is available.

Enable Safe Mode

Only essential drivers and services (e.g., generic mouse, monitor, base storage device, keyboard, video drivers, and the Event Log service) load when a computer boots in Safe Mode. This allows you to troubleshoot misbehaving applications, services, and drivers.

Pre-EFI Initialization

PEI initializes the system and prepares for the Driver Execution Environment (DXE). 1. The CPU and chipset are verified and fully initialized. 2. System memory is initialized, verified, and allocated. 3. PEI modules are loaded to allocate system resources. 4. The DXE is initialized, and the system is prepared to transition to DXE.

Which option is the first process that runs once a computer is powered on and the CPU loads the BIOS? WININIT Boot Loader POST Winload.exe

POST Explanation On a system using BIOS, the computer powers on, and then the CPU loads the BIOS. The first process to run is the Power-On Self Test (POST). Boot loader, Winload.exe, and WININIT load after POST.

What are the general stages of the Windows startup process?

POST, Bootloader, OS Load, Driver load, User Login.

bootrec/fixmbr (in Bootreq, recovery mode -> cmd)

Part of the Recovery Console that writes a new master boot record to a disk. - fixes a corrupt mbr - fixes windows won't boot error

Enable Safe Mode with Command Prompt

Safe Mode with Command Prompt starts the computer in safe mode and displays a command prompt.

Enable Safe Mode with Networking

Safe Mode with Networking is a variation of Safe Mode that also loads a network driver and protocol so the system can communicate on the network. This option is useful when you must download an updated driver from the internet and install it on the system to correct a problem.

sfc /scanfile

Scans a file that you specify and fixes problems if they are found.

sfc /scannow

Scans integrity of all protected system files and repairs files with problems when possible.

sfc /verifyonly

Scans protected system files and does not make any repairs or changes

Disable Driver Signature Enforcement

Selecting this option causes Windows to not require a digital signature when loading a driver.

Corrupt MBR or partition table

Symptoms of a corrupt MBR or partition table include: - The system hangs immediately after the BIOS information displays. - Any of the following errors: * MBR corrupt. * Invalid partition table. * Error loading operating system. * Missing operating system. To fix the problem, boot the system from the installation disc and repair the system.

Marcus was attempting to edit some registry settings on his Windows 11 system. Now, when he tries to boot his system, it hangs after the Windows splash screen is displayed. Because he cannot boot to Safe Mode, he boots the system from the Windows installation disc and accesses the Recovery Environment. Which Recovery option should Marcus use FIRST to help resolve his boot issue? Use BOOTMGR Reset this PC System Restore Go Back to the Previous Build

System Restore Explanation The most common cause of the system hanging after the Windows splash screen is displayed is a bad driver or corrupt registry settings. If you cannot boot to Safe Mode, boot into the Recovery Environment and use System Restore. Resetting the PC or going back to a previous build might also work, but these are more drastic options. You should try simpler recovery options first before moving on to more drastic ones. BOOTMGR is the boot loader program. It is not a recovery option.

Which of the following actions occur during the Pre-EFI Initialization (PEI) stage of the UEFI boot process? (Select two.) The CPU and chipset are verified and fully initialized. Power is supplied to the CPU. The EFI boot manager initializes. System memory is initialized, verified, and allocated. Device drivers are loaded into memory.

The CPU and chipset are verified and fully initialized. System memory is initialized, verified, and allocated. Explanation During the PEI stage of the UEFI boot process, the CPU and chipset are verified and fully initialized, and system memory is initialized, verified, and allocated. Device drivers are loaded into memory and the EFI boot manager initializes during the DXE (Driver Execution Environment) stage, which comes after the PEI stage. Power is supplied to the CPU during the Security (SEC) stage, which comes before the PEI stage.

Inaccessible boot disk

The boot loader program uses the boot configuration database (BCD) to locate valid Windows installations to start. If the database points to a location that does not include any operating system files, you will see a message similar to the following: Windows could not start because of a computer disk hardware configuration problem. Could not read from the selected boot disk. Check boot path and disk hardware. To correct the problem, boot the system from the installation disc and repair the system. 1. Boot from the installation DVD (or the recovery USB). 2. At the Welcome screen, select Repair your computer. 3. Select Troubleshoot. 4. Select Command Prompt. 5. When the Command Prompt loads, type the following command: bootrec /RebuildBcd (The /RebuildBcd option causes the bootrec command to scan all storage devices for operating systems and add them to the BCD database.)

Master Boot Record (MBR)

The first sector on a hard drive, which contains the partition table and a program the BIOS uses to boot an OS from the drive.

Blue/black screen or system hangs after Windows splash screen is displayed

The most common cause of the errors is bad drivers or corrupt registry settings. To correct the problem, try the following (in this order): * If the error includes any error codes or messages, check the Microsoft website for troubleshooting information. * If you can, boot the system into Safe Mode. In Safe Mode, roll back drivers, remove drivers, or restore to a restore point. * To identify the driver causing the problem, enable boot logging, then read the Ntbtlog.txt file to identify the last driver that the system tried to load. * If you cannot boot into Safe Mode, boot into the Recovery Environment and use System Restore to restore to a restore point created when the system was working correctly.

Device fails to start

This message indicates that a hardware device could not be started. Begin by checking Device Manager for information about the device. If necessary, update the driver or disable the device.

Enable Boot Logging

This option creates a log file named Ntbtlog.txt in C:\Windows during startup. This file contains an entry for each driver loaded during the boot process. If the system does not complete a regular boot, you can look at this file to see the last driver to load before the failure occurs.

Enable Low-Resolution Video

This option loads Windows using the current video driver but configures it to use low-resolution settings and a slow refresh rate. This option is useful when the wrong video configuration settings cause the screen to be unreadable. Selecting this option gives you the ability to restore the correct video settings.

Disable Early Launch Anti-Malware Protection

This option prevents the early launch anti-malware driver from loading when you boot the system. This could increase the system's exposure to rootkit malware packages.

Enable Debugging (Advanced Start-up Mode)

This option starts Windows in an advanced troubleshooting mode. Programmers, not administrators, typically use this option.

bootrec /fixboot

To attempt repair of the boot sector. Also writes a new boot sector.

How do you correct a corrupt MBR or partition table?

To start the partition table repair process, type "bootrec.exe/fixmbr" in the command prompt and press "Enter". This command will perform a quick fix on the lost or damaged partition table.

UEFI Boot

UEFI is a newer boot specification that defines the software interface between an operating system and the computer's firmware. The following diagram and table describe the stages of the UEFI boot sequence.

Launch Recovery Environment

Use this option to access system recovery tools, such as: * System Restore * System Image Recovery * Startup Repair * Command Prompt * Go Back to the Previous Build Options may differ depending on the device.

Your Windows 11 system powers on, but there is no image on your display. You have already checked to make sure that the monitor is connected properly to the computer, is plugged in, and is turned on. Which of the following is the BEST next step you should take to try to resolve the issue? Check the motherboard documentation for information on beeps. Verify that the BIOS/UEFI is configured to use the correct video adapter. Boot the system from the installation disc and repair the system. Use System Restore from Safe Mode to select a working restore point.

Verify that the BIOS/UEFI is configured to use the correct video adapter. Explanation You should verify that the BIOS/UEFI is configured to use the correct video adapter. You can configure most motherboards to use either the integrated video adapter or a PCIe video adapter installed in an expansion slot. While a series of beeps produced by the motherboard can indicate a specific problem when there is no display on the monitor, there may be no beeps in this scenario, or the beeps may not indicate a problem with the display. While using one of the recovery options from the installation disc might help, it is much easier to first check the BIOS/UEFI to make sure that the correct video adapter is configured for the monitor. While returning the Windows 11 system to a previous restore point might help (such as with a display driver issue), in this scenario, it is more likely that the correct video adapter is not configured in the BIOS/UEFI.

BIOS Boot

Windows systems can boot using either a legacy BIOS or a UEFI boot sequence. Understanding these boot sequences enables you to focus troubleshooting efforts on the most likely errors. The following diagram and table describe the four basic stages of the Legacy BIOS boot sequence:

Which symptoms may indicate a corrupt or missing boot sector?

You would not be able to boot your PC, or the PC would boot on a drive other than expected. Or you might get the BIOS message that the OS is missing.

You are troubleshooting a Windows 11 system that won't boot. The system appears to initialize just fine, and POST completes correctly. However, Windows does not load, and an error message is displayed on the screen, indicating that the operating system is not found. You determine that the Master Boot Record (MBR) is corrupt. To fix the issue, you perform the following steps: Boot the system from the Windows 11 installation DVD. Access the Recovery Environment. Open a Command Prompt window. Enter the command that you should run at the Command Prompt to address this issue. _________________________

bootrec /fixmbr Explanation The bootrec /fixmbr command writes a Windows-compatible MBR to the system partition. This command does not overwrite the existing partition table. Use this method when you need to resolve MBR corruption issues or when you have to remove non-standard code from the MBR.